Cargo vehicles, such as semi-trailers, van-type trailers, flatbed or platform type trailers, container chassis and cargo containers, are known. Cargo vehicles include articulated vehicles which have a permanent or semi-permanent pivoting joint as part of the vehicle's structure. The forward underbody of a trailer includes an upper coupler assembly having a kingpin configured to couple the trailer to a fifth wheel (also known as a lower coupler) of the tractor.
When in motion, the upper coupler assembly of a trailer is subjected to a spray of road debris from the tractor's tires which may include sand, gravel, ice and snow, as well as the chemicals used to remove snow and ice. This spray of various materials promotes corrosion of the upper coupler assembly which acts on both its external and internal surfaces. Historically, trailer upper coupler assemblies have been coated externally and internally with a variety of well known materials and methods (the usual coatings are alkyd and epoxy paints and “undercoatings” such as sulfonated wax systems or water emulsified asphaltic coatings).
Galvanizing is a well-known method to protect against corrosion. However, the kingpin used in semi-trailers is typically made of alloy steel heat treated by quenching and subsequent tempering to achieve appropriate strength and wear resistance. If subjected to the galvanization process, a kingpin may lose its strength and wear resistance or become subject to hydrogen embrittlement as a result of the plating process.
It is the purpose of this invention to provide a partially galvanized upper coupler, which is also usable with the lower coupler on the truck tractor.